Mesoscale Discussion 1122
NWS Storm Prediction Center Norman OK
1218 PM CDT Thu Jun 22 2017
Areas affected...Portions of northeastern OH...western/central
PA...and western NY
Concerning...Severe potential...Watch unlikely
Valid 221718Z - 221945Z
Probability of Watch Issuance...20 percent
SUMMARY...An isolated threat for strong to locally damaging winds
and marginally severe hail may persist through the afternoon.
Overall threat should remain too marginal for watch issuance.
DISCUSSION...17Z objective analysis of surface observations
indicates a warm front is draped from southeastern lower MI across
Lake Erie into western NY and northern PA. The airmass along/south
of the front has become weakly unstable early this afternoon, with
MLCAPE generally ranging 500-1000 J/kg per 17Z RAP Mesoanalysis.
Further diurnal heating may allow for MLCAPE values to approach 1500
J/kg across parts of western/central PA through 20Z. In association
with a weak mid-level disturbance embedded within strong westerly
flow at mid/upper levels, isolated thunderstorms have developed
across eastern Lake Erie into parts of far western NY and
northwestern PA. One of these cells exhibited brief supercell
characteristics before weakening across Butler into Armstrong County
PA.
Most of western NY into into western/central PA and northeastern OH
will remain displaced to the south of stronger mid-level flow across
the upper Great Lakes into southern Ontario/Quebec and New England.
Still, around 30-35 kt of westerly flow at 500 mb will support
similar values of effective bulk shear through the afternoon across
this region. Additional convective development across northeastern
OH along the shore of Lake Erie will be possible over the next
several hours, and any thunderstorms that can remain along/south of
the front will have the potential to be surface-based. Given the
marginal shear values, multicells will probably be the dominant
storm mode, posing a strong to locally damaging wind and perhaps
marginally severe hail threat. The lack of even stronger instability
(mainly owing to weak mid-level lapse rates) and shear will likely
preclude a more robust severe weather threat through the remainder
of the afternoon. Accordingly, watch issuance is unlikely at this
time.
..Gleason/Guyer.. 06/22/2017
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...BGM...BUF...CTP...PBZ...CLE...
LAT...LON 40868152 41628174 41858144 42287998 42807896 42467614
41417621 40487713 40407925 40868152